Enabling very large and very small duty cycles in switching converters

ABSTRACT

In accordance with embodiments of the present disclosure, an apparatus may include a switched-mode power supply and a controller. The switched-mode power supply may include an inductor and a plurality of switches coupled to the inductor. The controller may be configured to control an inductor current of the inductor by controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.

RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional Patent Application Ser. No. 62/255,960, filed Nov. 16, 2015, which is incorporated by reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates in general to circuits for audio devices, including without limitation personal audio devices such as wireless telephones and media players, and more specifically, to a switched mode power supply for supplying a supply voltage to an amplifier or other load.

BACKGROUND

Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers. Generally speaking, a power amplifier amplifies an audio signal by taking energy from a power supply and controlling an audio output signal to match an input signal shape but with a larger amplitude. Although many amplifier architectures (e.g., Class A, Class B, and Class AB amplifiers) provide for only a single power supply for a power amplifier, some architectures provide for at least two supply voltages for powering a power amplifier, in order to achieve greater power efficiency over single or constant power supply voltage architectures.

One example of a multi-supply voltage amplifier is a Class H amplifier. A Class H amplifier may have an infinitely variable voltage supply rail that tracks an envelope of an output signal of the Class H amplifier. In order to provide such an infinitely variable voltage supply rail, the output supply rail may be modulated such that the rail is only slightly larger than a magnitude of the audio output signal at any given time. For example, switched-mode power supplies may be used to create the output signal-tracking voltage rails. Accordingly, a Class H amplifier may increase efficiency by reducing the wasted power at output driving transistors of the amplifier.

Such amplifiers often utilize switched-mode power supplies for drawing a supply voltage. Switched-mode power supplies may include power converters for converting one direct-current voltage (e.g., provided by a battery or other power source) to another direct-current voltage. For example, buck converters are often used to generate voltages lower than the source (e.g., battery) voltage, and boost converters are often used to generate voltages higher than the source (e.g., battery) voltage. However, for both buck and boost converters, generating a voltage that is close to the power source voltage is challenging due to the extremely large or small duty cycles needed to do so. Realizing such small duty cycles using switches may require some of the switches to be activated (e.g., enabled, turned on, closed) for infinitesimally small periods of time.

One solution to this challenge is to use a buck-boost converter when a voltage close to the power source voltage is desired. However, buck-boost converters are often power inefficient. Another solution is to use a multi-mode converter which operates in a buck mode at lower output voltages, a boost mode at higher output voltages, and a buck-boost mode at voltages near the power source voltage. However, transitions between the various modes are challenging, as the average inductor current in each of the modes is different, which may lead to large discontinuities when transitioning from one mode to another. Such transitioning can be especially difficult in certain applications such as Class H amplifiers in which accurate tracking supply rails are desired.

SUMMARY

In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with existing approaches to driving an audio output signal to an audio transducer may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a method of controlling an inductor current in a switched-mode power supply having a plurality of switches may include controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.

In accordance with these and other embodiments of the present disclosure, an apparatus may include a switched-mode power supply and a controller. The switched-mode power supply may include an inductor and a plurality of switches coupled to the inductor. The controller may be configured to control an inductor current of the inductor by controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.

Technical advantages of the present disclosure may be readily apparent to one skilled in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIG. 1 is an illustration of an example personal audio device, in accordance with embodiments of the present disclosure;

FIG. 2 is a block diagram of selected components of an example audio integrated circuit of a personal audio device, in accordance with embodiments of the present disclosure;

FIG. 3 is a block diagram of selected components of an example buck converter, in accordance with embodiments of the present disclosure;

FIG. 4A illustrates possible connections among components of the buck converter of FIG. 3 for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure;

FIG. 4B illustrates additional possible connections among components of the buck converter of FIG. 3 for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure;

FIG. 5 is a block diagram of selected components of an example boost converter, in accordance with embodiments of the present disclosure;

FIG. 6 illustrates possible connections among components of the boost converter of FIG. 5 for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure;

FIG. 7 is a block diagram of selected components of an example multi-phase power converter, in accordance with embodiments of the present disclosure;

FIG. 8 illustrates possible connections among components of the multi-phase power converter of FIG. 7 for each of four phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure;

FIG. 9A illustrates a graph of an example inductor current for each of four phases of operation of the multi-phase power converter of FIG. 7, in accordance with embodiments of the present disclosure; and

FIG. 9B illustrates a another graph of an example inductor current for each of four phases of operation of the multi-phase power converter of FIG. 7, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is an illustration of an example personal audio device 1, in accordance with embodiments of the present disclosure. FIG. 1 depicts personal audio device 1 coupled to a headset 3 in the form of a pair of earbud speakers 8A and 8B. Headset 3 depicted in FIG. 1 is merely an example, and it is understood that personal audio device 1 may be used in connection with a variety of audio transducers, including without limitation, headphones, earbuds, in-ear earphones, and external speakers. A plug 4 may provide for connection of headset 3 to an electrical terminal of personal audio device 1. Personal audio device 1 may provide a display to a user and receive user input using a touch screen 2, or alternatively, a standard liquid crystal display (LCD) may be combined with various buttons, sliders, and/or dials disposed on the face and/or sides of personal audio device 1. As also shown in FIG. 1, personal audio device 1 may include an audio integrated circuit (IC) 9 for generating an analog audio signal for transmission to headset 3 and/or another audio transducer.

FIG. 2 is a block diagram of selected components of an example audio IC 9 of a personal audio device, in accordance with embodiments of the present disclosure. In some embodiments, example audio IC 9 may be used to implement audio IC 9 of FIG. 1. As shown in FIG. 2, a microcontroller core 18 may supply a digital audio input signal DIG_IN to a digital-to-analog converter (DAC) 14, which may convert the digital audio input signal to an analog signal V_(IN). DAC 14 may supply analog signal V_(IN) to an amplifier stage 16 which may amplify or attenuate audio input signal V_(IN) to provide an audio output signal V_(OUT), which may operate a speaker, headphone transducer, a line level signal output, and/or other suitable output. A capacitor CO may be utilized to couple the output signal to the transducer or line level output, particularly if amplifier stage 16 is operated from a unipolar power supply having a quiescent voltage substantially differing from ground. Also, as shown in FIG. 2, audio IC 9 may include a control circuit 20 configured to, based on digital audio input signal DIG_IN, control a power supply voltage of amplifier stage 16 using one or more control signals (labeled as “VOLTAGE CONTROL” in FIG. 2).

As depicted in FIG. 2, amplifier stage 16 may include any suitable amplifier 26 which has an input for receiving analog signal V_(IN), an output for generating output signal V_(OUT) based on and indicative of analog signal V_(IN), and a power supply input for receiving a load voltage V_(LOAD) output by a power supply 28, wherein power supply 28 outputs load voltage V_(LOAD) regulated by one or more control signals VOLTAGE CONTROL. In some embodiments, load voltage V_(LOAD) output by power supply 28 may be variable in that it is selected from a plurality of discrete voltages, or includes an infinite number of voltages between a minimum and maximum voltage. In some embodiments, power supply 28 may be implemented with a switched-mode power supply, such as, but not limited to, buck converter 30 depicted in FIG. 3, boost converter 50 depicted in FIG. 5, or multi-phase power converter 70 depicted in FIG. 7.

FIG. 3 is a block diagram of selected components of an example buck converter 30, in accordance with embodiments of the present disclosure. As shown in FIG. 3, buck converter 30 may include or may be coupled to a battery 38 or other voltage source configured to output a battery voltage V_(BAT). Battery 38 may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery 38. As shown in FIG. 3, buck converter 30 may also include an output at which buck converter 30 may generate a single-ended load voltage V_(LOAD).

Buck converter 30 may comprise a power inductor 36 and a plurality of switches 31-35. Power inductor 36 may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor 36, in accordance with Faraday's law of electromagnetic induction, which opposes the change in current that created the magnetic field.

Each switch 31-35 may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches 31-35 (e.g., control signals communicated from control circuit 20) are not depicted although such control signals would be present to selectively enable and disable switches 31-35. In some embodiments, a switch 31-35 may comprise an n-type metal-oxide-semiconductor field-effect transistor.

Switch 31 may be coupled between a positive input terminal of battery 38 and a first terminal of power inductor 36. Switch 32 may be coupled between a negative input terminal of battery 38 (e.g., a ground voltage) and the first terminal of power inductor 36. Switch 33 may be coupled between the positive input terminal of battery 38 and a second terminal of power inductor 36. Switch 34 may be coupled between the negative input terminal of battery 38 and the second terminal of power inductor 36. Switch 55 may be coupled between the second terminal of power inductor 36 and an output terminal of buck converter 30.

In operation, switches 31-35 may be controlled by control circuit 20 such that buck converter 30 sequentially operates in a plurality of phases as shown in either of FIG. 4A or FIG. 4B, the length of each phase controlled in order to regulate a desired load voltage V_(LOAD) less than battery voltage V_(BAT). As shown in FIG. 4A, buck converter 30 may operate in a repeating sequence of a charging phase T1, a discharge phase T2, and a hold phase T3. In charging phase T1, switches 31 and 35 may be activated (e.g., enabled, turned on, closed) and switches 32, 33, and 34 may be deactivated (e.g., disabled, turned off, opened). In discharging phase T2, switches 32 and 35 may be activated and switches 31, 33, and 34 may be deactivated. In hold phase T3, switches 31 and 33 may be activated and switches 32, 34, and 35 may be deactivated. Accordingly, an inductor current I_(L) flowing through power inductor 36 may increase during charging phase T1, decrease during discharging phase T2, and remain substantially constant during hold phase T3.

Thus, when a duration of hold phase T3 is sufficiently large, a duration of charging phase T1 may be made infinitesimally small, because as buck converter 30 sequences from hold phase T3 to charging phase T1 to discharging phase T2, switches on opposite sides of inductor 36 need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of charging phase T1 may enable buck converter 30 to generate arbitrary small voltages (e.g., near zero) for load voltage V_(LOAD), which is often difficult using traditional approaches.

Similarly, as shown in FIG. 4B, buck converter 30 may operate in a repeating sequence of a charging phase T1, a discharge phase T2, and a hold phase T3. In charging phase T1, switches 31 and 35 may be activated (e.g., enabled, turned on, closed) and switches 32, 33, and 34 may be deactivated (e.g., disabled, turned off, opened). In discharging phase T2, switches 32 and 35 may be activated and switches 31, 33, and 34 may be deactivated. In hold phase T3, switches 32 and 34 may be activated and switches 31, 33, and 35 may be deactivated. Accordingly, an inductor current I_(L) flowing through power inductor 36 may increase during charging phase T1, decrease during discharging phase T2, and remain substantially constant during hold phase T3.

Thus, when a duration of hold phase T3 is sufficiently large, a duration of discharge phase T2 may be made infinitesimally small, because as buck converter 30 sequences from charging phase T1 to discharge phase T2 to hold phase T3, switches on opposite sides of inductor 36 need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of discharge phase T2 may enable buck converter 30 to generate voltages near that of battery voltage V_(BAT) for load voltage V_(LOAD), which is often difficult using traditional approaches.

FIG. 5 is a block diagram of selected components of an example boost converter 50, in accordance with embodiments of the present disclosure. As shown in FIG. 5, boost converter 50 may include or may be coupled to a battery 58 or other voltage source configured to output a battery voltage V_(BAT). Battery 58 may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery 58. As shown in FIG. 5, boost converter 50 may also include an output at which boost converter 50 may generate a single-ended load voltage V_(LOAD).

Boost converter 50 may comprise a power inductor 56 and a plurality of switches 51-54. Power inductor 56 may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor 56, in accordance with Faraday's law of electromagnetic induction, which opposes the change in current that created the magnetic field.

Each switch 51-54 may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches 51-54 (e.g., control signals communicated from control circuit 20) are not depicted although such control signals would be present to selectively enable and disable switches 51-54. In some embodiments, a switch 51-54 may comprise an n-type metal-oxide-semiconductor field-effect transistor.

Switch 51 may be coupled between a positive input terminal of battery 58 and a first terminal of power inductor 56. Switch 52 may be coupled between a negative input terminal of battery 58 (e.g., a ground voltage) and the first terminal of power inductor 56. Switch 53 may be coupled between a second terminal of power inductor 56 and the output terminal of boost converter 50. Switch 54 may be coupled between the negative input terminal of battery 58 and the second terminal of power inductor 56.

In operation, switches 51-54 may be controlled by control circuit 20 such that boost converter 50 sequentially operates in a plurality of phases as shown in FIG. 6, the length of each phase controlled in order to regulate a desired load voltage V_(LOAD) greater than battery voltage V_(BAT). As shown in FIG. 6, boost converter 50 may operate in a repeating sequence of a charging phase T1, a transfer phase T2, and a hold phase T3. In charging phase T1, switches 51 and 54 may be activated and switches 52 and 53 may be deactivated. In transfer phase T2, switches 51 and 53 may be activated and switches 52 and 54 may be deactivated. In hold phase T3, switches 52 and 54 may be activated and switches 51 and 53 may be deactivated. Accordingly, an inductor current I_(L) flowing through power inductor 56 may increase during charging phase T1, decrease during transfer phase T2, and remain substantially constant during hold phase T3.

Accordingly, when a duration of hold phase T3 is sufficiently large, a duration of charging phase T1 may be made infinitesimally small, because as boost converter 50 sequences from hold phase T3 to charging phase T1 to transfer phase T2, switches on opposite sides of inductor 56 need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of charging phase T1 may enable boost converter 50 to generate voltages for load voltage V_(LOAD) which are arbitrary close to battery voltage V_(BAT), which is often difficult using traditional approaches.

FIG. 7 is a block diagram of selected components of an example multi-phase power converter 70, in accordance with embodiments of the present disclosure. As shown in FIG. 7, multi-phase power converter 70 may include or may be coupled to a battery 78 or other voltage source configured to output a battery voltage V_(BAT). Battery 78 may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery 78. As shown in FIG. 7, multi-phase power converter 70 may also include an output at which multi-phase power converter 70 may generate a single-ended load voltage V_(LOAD).

Multi-phase power converter 70 may comprise a power inductor 76 and a plurality of switches 71-74. Power inductor 76 may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor 76, in accordance with Faraday's law of electromagnetic induction, which opposes the change in current that created the magnetic field.

Each switch 71-74 may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches 71-74 (e.g., control signals communicated from control circuit 20) are not depicted although such control signals would be present to selectively enable and disable switches 71-74. In some embodiments, a switch 71-74 may comprise an n-type metal-oxide-semiconductor field-effect transistor.

Switch 71 may be coupled between a positive input terminal of battery 78 and a first terminal of power inductor 76. Switch 72 may be coupled between a negative input terminal of battery 78 (e.g., a ground voltage) and the first terminal of power inductor 76. Switch 73 may be coupled between a second terminal of power inductor 76 and the output terminal of multi-phase power converter 70. Switch 74 may be coupled between the negative input terminal of battery 78 and the second terminal of power inductor 76.

In operation, switches 71-74 may be controlled by control circuit 20 such that multi-phase power converter 70 sequentially operates in a plurality of phases as shown in FIG. 8, the length of each phase controlled in order to regulate a desired load voltage V_(LOAD). As shown in FIG. 8, multi-phase power converter 70 may operate in a repeating sequence of a charging phase T1, a bridge phase T2, a discharging phase T3, and a hold phase T4. In charging phase T1, switches 71 and 74 may be activated and switches 72 and 73 may be deactivated. In bridge phase T2, switches 71 and 73 may be activated and switches 72 and 74 may be deactivated. In discharging phase T3 switches 72 and 73 may be activated and switches 71 and 74 may be deactivated. In hold phase T4, switches 72 and 74 may be activated and switches 71 and 73 may be deactivated. Accordingly, as shown in FIG. 9A, an inductor current I_(L) flowing through power inductor 76 may increase during charging phase T1, increase during bridge phase T2 (e.g., if battery voltage V_(BAT) is greater than load voltage V_(LOAD)), decrease during discharge phase T3, and remain substantially constant during hold phase T4. Alternatively, as shown in FIG. 9B, an inductor current I_(L) flowing through power inductor 76 may increase during charging phase T1, decrease during bridge phase T2 (e.g., if battery voltage V_(BAT) is lesser than load voltage V_(LOAD)), decrease during discharge phase T3, and remain substantially constant during hold phase T4.

Thus, successive phase transitions have switches toggling on opposite sides of power inductor 76. For example, when transitioning from phase T1 to phase T2 phase, switches 74 and 73 on the second terminal of power inductor 76 toggle. When transitioning from phase T2 to phase T3, switches 71 and 72 on the first terminal of power inductor 76 toggle. Similar patterns are observed when transitioning from phase T3 to phase T4 and from phase T4 to phase T1. Thus, each pair of successive transitions involves toggling switches on opposite terminals of power inductor 76. Thus, in successive transitions, the same switch does not have to toggle. Now, as long as a duration of phase T4 phase is sufficiently large, the durations of any of phase T1, phase T2, or phase T3 may be infinitesimally small. This is because the same switch does not have to toggle when going from one phase to another.

Although the foregoing contemplates one of buck converter 30, boost converter 50, or multi-phase power converter 70 used to implement power supply 28, power supply 28 may be implemented using any suitable switched-mode power supply (including a multi-mode switched-mode power supply capable of operating in a plurality of modes including a buck mode, a boost mode, and/or a buck-boost mode).

In addition, although the foregoing describes a hold phase in which an inductor current remains constant, in some embodiments, such hold phase may result in an increase or decrease in inductor current.

As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements.

This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.

All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure. 

What is claimed is:
 1. A method of controlling an inductor current in a switched-mode power supply having a plurality of switches, comprising controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.
 2. The method of claim 1, wherein the first phase and the second phase occur successively.
 3. The method of claim 1, wherein the first phase and the second phase occur non-successively.
 4. The method of claim 1, wherein the first period is defined by a difference in time between switching of at least two switches of the plurality of switches, and the first period occurs immediately before or after a third period of the at least three phases.
 5. The method of claim 1, wherein the second period is defined by a difference in time between switching of at least two switches of the plurality of switches, and the second period occurs immediately before or after a third period of the at least three phases.
 6. The method of claim 1, the at least three phases comprising a third phase in which the inductor current remains substantially constant.
 7. The method of claim 1, the at least three phases comprising a third phase in which the inductor current increases.
 8. The method of claim 7, the at least three phases comprising a fourth phase in which the inductor current remains substantially constant.
 9. The method of claim 7, the at least three phases comprising a fourth phase in which the inductor current increases.
 10. The method of claim 7, the at least three phases comprising a fourth phase in which the inductor current decreases.
 11. The method of claim 1, the at least three phases comprising a third phase in which the inductor current decreases.
 12. The method of claim 11, the at least three phases comprising a fourth phase in which the inductor current remains substantially constant.
 13. The method of claim 11, the at least three phases comprising a fourth phase in which the inductor current increases.
 14. The method of claim 11, the at least three phases comprising a fourth phase in which the inductor current decreases.
 15. An apparatus comprising: a switched-mode power supply comprising: an inductor; and a plurality of switches coupled to the inductor; and a controller configured to control an inductor current of the inductor by controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.
 16. The apparatus of claim 15, wherein the first phase and the second phase occur successively.
 17. The apparatus of claim 15, wherein the first phase and the second phase occur non-successively.
 18. The apparatus of claim 15, wherein the first period is defined by a difference in time between switching of at least two switches of the plurality of switches, and the first period occurs immediately before or after a third period of the at least three phases.
 19. The apparatus of claim 15, wherein the second period is defined by a difference in time between switching of at least two switches of the plurality of switches, and the second period occurs immediately before or after a third period of the at least three phases.
 20. The apparatus of claim 15, the at least three phases comprising a third phase in which the inductor current remains substantially constant.
 21. The apparatus of claim 15, the at least three phases comprising a third phase in which the inductor current increases.
 22. The apparatus of claim 21, the at least three phases comprising a fourth phase in which the inductor current remains substantially constant.
 23. The apparatus of claim 21, the at least three phases comprising a fourth phase in which the inductor current increases.
 24. The apparatus of claim 21, the at least three phases comprising a fourth phase in which the inductor current decreases.
 25. The apparatus of claim 15, the at least three phases comprising a third phase in which the inductor current decreases.
 26. The apparatus of claim 25, the at least three phases comprising a fourth phase in which the inductor current remains substantially constant.
 27. The apparatus of claim 25, the at least three phases comprising a fourth phase in which the inductor current increases.
 28. The apparatus of claim 25, the at least three phases comprising a fourth phase in which the inductor current decreases. 